This invention relates generally to electric cooking appliances heating a cooking utensils such as cooking pans containing foodstuff to be cooked, and more particularly to such an electric cooking appliance employing a heater lamp as a heat source.
A halogen lamp is generally employed as a heater lamp in electric cooking appliances of the type described above which have recently been tried to be practiced. More specifically, the electric cooking appliance generally comprises a heating unit including a plurality of groups of halogen lamps, each group being made up of a plurality of halogen lamps, and a heat insulator covering the peripheral and bottom sides of the halogen lamps, and a top plate formed from a heat-proof glass having a good heat transmission property and covering the top opening of the heat insulator, thereby providing for construction with small heat loss. In use, a cooking pan or the like containing foodstuff is placed on the top plate and the heat generated by the halogen lamps is applied to the cooking pan so that the foodstuff contained in it is cooked.
In the above-described electric cooking appliance, heat generated by the halogen lamps is radiated or transmitted through the top plate to the cooking pan and accordingly a heated object contained in it. Since the heat capacity of the cooking pan is rendered relatively large, the temperature of the cooking pan is not raised so rapidly at an initial stage of the heating and the rise characteristic of the cooking pan temperature is lowered. Consequently, the halogen lamps of the high output type (usually 2 kW) have been conventionally employed as the heater lamps so that the cooking pan temperature is raised rapidly.
On the other hand, the heat insulator and the top plate are closely disposed for the purpose of enhancing the heating efficiency in the above-described electric cooking appliance and consequently, the interior of the heating unit is rendered a sealed space. For this reason, when the halogen lamps are continuously energized with the output of each of them maintained at a high level, the ambient temperature of the halogen lamps or an atmospheric temperature in the heating unit is gradually increased to exceed the critical heat proof temperature (about 850.degree. C.) of a quartz glass tube constituting the bulbs of the halogen lamps. In order to solve this problem, the conventional electric cooking appliance is provided with a thermostat as temperature sensing means for sensing the atmospheric temperature of the heating unit interior. The thermostat operates to deenergize the halogen lamps when the atmospheric temperature of the heating unit interior is increased to a predetermined value.
Making a good choice of the cooking pan is necessary in cooking with the above-described electric cooking appliance employing the halogen lamps. More specifically, the heat generated by the halogen lamps is radiated or transmitted through the top plate to the cooking pan and the heated object, as described above. An amount of heat transmitted to the cooking pan depends largely upon the material or configuration of the cooking pan used. The amount of heat transmitted to the cooking pan is increased as the material forming the cooking pan has a larger heat transfer coefficient and higher heat conductivity. Further, when the cooking pan has a flat bottom face, a contact area of the pan with the top plate is increased and accordingly, the heat transfer efficiency is increased, which increases the amount of heat transferred to the cooking pan. The heat generated by the halogen lamps is absorbed by the cooking pan more efficiently as the amount of heat transferred to the cooking pan is increased more. Consequently, the temperature of each halogen lamp bulb is not so much increased and a cooking period of time is shortened. Contrarily, in the case where the cooking pan has a small heat transfer efficiency such that the amount of heat transferred to the pan is small, the temperature of the cooking pan is not so much increased even when the output of each halogen lamp is uselessly increased. In such a case the cooking period of time is lengthened and only the temperature of each halogen lamp bulb is raised, which shortens the life of each halogen lamp.
Thus, the life of the halogen lamp and the cooking period of time are influenced by the selection of the cooking pan to be used in the cooking with the above-described electric cooking appliance. Consequently, it has been desired for the user to ascertain whether or not the selected cooking pan is suitable for the electric cooking appliance.